How to solve "permission denied" error when running "do-release-upgrade"?

I'm trying to upgrade Ubuntu 18.04 to 20.04. sudo apt update && sudo apt upgrade returns 0 upgraded. sudo do-release-upgrade returns the following log:

Checking for a new Ubuntu release
Get:1 Upgrade tool signature [1554 B]                                                                               
Get:2 Upgrade tool [1337 kB]                                                                                        
Fetched 1339 kB in 0s (0 B/s)                                                                                       
authenticate 'focal.tar.gz' against 'focal.tar.gz.gpg' 
extracting 'focal.tar.gz'
mkdir: cannot create directory '/run/user/0': Permission denied
[26749:0126/190654.793003:FATAL:atom_main_delegate.cc(210)] Running as root without --no-sandbox is not supported. See https://crbug.com/638180.

Traceback (most recent call last):
  File "/tmp/ubuntu-release-upgrader-dzkq9w82/focal", line 8, in <module>
    sys.exit(main())
  File "/tmp/ubuntu-release-upgrader-dzkq9w82/DistUpgrade/DistUpgradeMain.py", line 222, in main
    run_new_gnu_screen_window_or_reattach()
  File "/tmp/ubuntu-release-upgrader-dzkq9w82/DistUpgrade/DistUpgradeMain.py", line 196, in run_new_gnu_screen_window_or_reattach
    os.execv("/usr/bin/screen", cmd)
FileNotFoundError: [Errno 2] No such file or directory
Error in sys.excepthook:
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/problem_report.py", line 497, in add_to_existing
    self.write(f)
  File "/usr/lib/python3/dist-packages/problem_report.py", line 452, in write
    crc = zlib.crc32(block, crc)
TypeError: a bytes-like object is required, not 'str'

Original exception was:
Traceback (most recent call last):
  File "/tmp/ubuntu-release-upgrader-dzkq9w82/focal", line 8, in <module>
    sys.exit(main())
  File "/tmp/ubuntu-release-upgrader-dzkq9w82/DistUpgrade/DistUpgradeMain.py", line 222, in main
    run_new_gnu_screen_window_or_reattach()
  File "/tmp/ubuntu-release-upgrader-dzkq9w82/DistUpgrade/DistUpgradeMain.py", line 196, in run_new_gnu_screen_window_or_reattach
    os.execv("/usr/bin/screen", cmd)
FileNotFoundError: [Errno 2] No such file or directory

How to solve this problem? Please let me know if you need more information.

I removed screen installed by snap and installed it with apt. That solved the problem. Thanks!

^{Answer from OP's comment}